Browse Articles

The study of modification by melt alloying of recovered polypropylene with styrene and a-methylstyrene-diene block-copolymers is presented in this paper. The block-copolymers were synthetized with the same composition and molecular weight in order to relieve more accurately the influence of the component block nature upon the modification degree of the polyolefin. It was found that only the nature of the diene block has a significant influence on the intensity of the modification degree for recovered polypropylene. Keywords: recovered polypropylene, styrene-isoprene block-copolymers (SIS), styrene-butadiene block-copolymers (SBS), a-methylstyrene-butadiene block-copolymers (aMeSBaMeS)

The present work reports on the synthesis and biomineralization capacity of hydrogel networks composed of Bombyx mori silk fibroin, polyacrylamide and carboxylated multiwall carbon nanotubes soaked in simulated body fluid. Hydrogels were fabricated by the polymerization of acrylamide and N,N’-methylenebisacrylamide in silk fibroin solution containing carboxylated multiwall carbon nanotubes with potassium persulphate/triethanol amine redox system as initiator. The incorporation of the fibroin and MWCNT-COOH within the polymer network was proved by FTIR spectroscopy. Swelling measurements in saline solution were performed to evaluate the behaviour of these hydrogels having various compositions. Biomineralization assays in simulated body fluid solution showed the presence of apatite-like crystals onto the surface of the materials. Beneficial effects upon biomeralization process of the carboxylated nanotubes were further discussed. Mechanical compressive tests revealed good strengths for the silk hydrogels depending on their composition. The results of this study lay down the fundament for the use of these silk fibroin biomaterials in bone tissue engineering applications. Keywords: silk fibroin, carbon nanotubes, biomineralization, apatite, compressive strength

Cellulose and polyhydroxyalkanoates, polymers from renewable resources, have been intensively studied for the last decades and they are the main topic of this paper. Bacterial cellulose pellicles (BC) were synthesized in static culture fermentations and ultrasounds were used to disintegrate them into fibers (us-BC). Microcrystalline cellulose (MCC) and us-BC were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) and infrared spectroscopy (ATR-FTIR) with a view toward their use in fully biodegradable and biocompatible polymer composites. Mechanical properties of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) modified with the two types of celluloses were also investigated. AFM images showed that big aggregates of BC fibers disappeared after ultrasound treatment but small aggregates coexist with separated fibers in us-BC sample. Higher XRD crystallinity and crystallite dimension were obtained for us-BC as compared to MCC. Mechanical tests on poly(3-hydroxybutyrate-co-3-hydroxyvalerate), neat and modified with the two cellulosic fillers, showed that the highest values of tensile strength and modulus were obtained in the case of the composite containing us-BC. Keywords: bacterial cellulose, polyhydroxyalkanoates, XRD, polymer composites, AFM

The paper presents experimental data regarding organic modified silica hybrids having embedded a non-ionic dye – Disperse Red 1, deposited on cotton fabrics. Hybrids were prepared by sol-gel processes using tetraethoxysilane and various trialkoxysilanes as organic network modifying agents, in acid catalysis and in the presence of Disperse Red 1. Control of the interactions between the organic non-ionic dyestuff and its embedding matrices allows tailoring the performance of the resulted coatings. Light and wash fastness and thermo-mechanical properties of the coated fabrics were investigated and correlated to the composition and morphology of the organic-inorganic coating materials. The results show that chemical composition of the impregnating bath have a decisive role in determining shade, intensity, fastness to light or washing of the coloured hybrid coatings as well as thermo-mechanical and hydrophobic properties of the coated textile fabrics. Keywords: silica hybrids, non-ionic dye, cotton fabrics, contact angle, thermal stability

The influence of various additives, like salts, alkohols, surfactants and water-miscible organic solvents, upon the cloud point of a, w - (2-hydroxyethoxy) oligo(propylene oxide) in aqueous solutions was investigated for the first time. The results showed that NaH2PO4, NaCl, NaBr, NaI, 1-butanol, ethylene glycol and dimethylsulfoxide decreased the cloud point, while 1,2-propylene glycol, sodium dodecylsulfate, nonylphenyl ethoxylated with 9 moles of ethylene oxide and dioxane increased it. Addition of N,N-dimethylformamide practically had no influence upon the cloud point on the concentration interval investigated. The LCST of a, w - (2-hydroxyethoxy) oligo(propylene oxide) in aqueous solution was also determined and it was found equal to 19°C. Keywords: a, w-(2-hydroxyethoxy) oligo(propylene oxide), thermosensitive polymers, cloud point, low critical solution temperature (LCST), additives

This paper presents new composite materials used in extension of growth season of vegetable crops, in countries with a mild continental transition climate, for constructions type tunnel. Composite materials are realized from two components, namely textile materials with generated heat potential and polyethylene polymer foils, with a selection possibility of wave lengths in IR domain. For insurance of microclimate conditions, especially of thermal performance, the materials have been tested from electrical and mechanical point of views, following the generated heat flux and its elastic deformations for a known material width. Keywords: tunnel, horticultural crops, composite materials

Alkylation of benzene with bioethanol (95% and 100% concentration) has been done in a laboratory tubular reactor using a new modified zeolitic catalyst. The alkylation experiments have been done at different reaction temperatures , pressures and benzene/bioetanol molar ratio in order to establish their influence on the final composition of the reaction product, selectivity and conversion. The feed and products are analysed by gas chromatography. There was small differences between 100% bioethanol and 95% bioethanol aqueous solution in experimental alkylation results that it possible to use 95% bioethanol solution as alkylating agent. Keywords: alkylation benzene, bioethanol, ethylbenzene, zeolitic catalyst

Rubber is widely used for rolling stock and railway infrastructure parts. Rubber plates are used for rail – sleeper fastening systems and rubber parts are used for primary suspension of the Romanian (and abroad) electrical locomotives, of metro (underground) trains, of tramways; at tramways wheels are made as metal – rubber assembly with the purpose to minimize the unsprung mass. From above examples, it easy to see that rubber parts are used in railway field as elements which are directly involved in safety of circulation. Keywords: tests, locomotive, primary suspensions, rubber-metal

The vulnerability of ordinary Portland cement (OPC) concrete to acidic attack is a worrying subject regarding the future durability of this binder. On the other side of binder’s technology, the new technology of cement called ‘geopolymer’ had been studied widely in all over the world. Indeed, the major advantage of geopolymer compared to Portland cement is chemical resistance. This paper presents a study about the microstructural properties of geopolymer and OPC mortar. Visual inspection of both mortars had been performed. Stereo microscope device and Secondary Electron Microscope (SEM) were used to investigate the microstructural changes of the specimens. It was found that geopolymer mortars were less susceptible to the attack by sulfuric acid solution than the OPC cement mortars. Keywords: geopolymer, sulfuric acid attack, microstructural, SEM

The wide band dielectric spectroscopy analysis of the 1.5% multi walled carbon nanotube (MWNT) contain and 20% polyamide 6 (PA6) nanowebs obtained by three different treatments applied to the MWNTs (chemical, mechanical and mixed) was investigated. A morphological analysis of the samples was carried out using the scanning electron microscopy (SEM) and atomic force microscopy (AFM) principles. The evolution of the dielectric constant (Eps’), imaginary permittivity (Eps”), dissipation factor (Tan d) and the conductivity modulus were analysed, both from an experimental and a theoretical point of view. Keywords: nanowebs, polyamide 6, multi walled carbon nanotubes, wide band dielectric spectroscopy